Solubilization of scandium from fluoride bearing materials

ABSTRACT

A method of selectively removing scandium from a scandium and fluoride-containing feed material includes providing the scandium-containing feed material, acid leaching the scandium-containing feed material with at least one acid in a presence of at least one of an aluminum or iron containing salt to form a scandium containing stream, and purifying the scandium containing stream to form a scandium compound end product.

FIELD OF THE INVENTION

The present invention relates generally to selectively recoveringscandium from solid materials, and more particularly to solubilizingscandium from fluoride bearing materials.

BACKGROUND

Scandium has gained importance for the use of scandium-stabilizedzirconia as a high efficiency electrolyte in solid oxide fuel cells.Applications of scandium also include use of scandium oxide (Sc₂O₃) tomake high-intensity discharge lamps, and scandium-aluminum alloys thatare used for minor aerospace industry components, baseball bats, andbicycle frames.

Due to limitations in mining and availability, scandium is currentlyonly produced in small quantities. While the element occurs in manyores, it is only present in trace amounts; there are no known,easily-extractable deposits of minerals containing high scandiumcontent. Thus, conventional acid recovery processes may be unsuitablefor processing fluoride containing scandium ores. As commercial uses forscandium continue to expand, there exists the need for the developmentof improved methods to selectively recover scandium from readilyavailable sources, such as ores in which a fluoride is present.

SUMMARY

An embodiment relates to a method of selectively removing scandium froma scandium-containing feed material which includes providing thescandium-containing feed material, acid leaching the scandium-containingfeed material with at least one acid in a presence of at least one of analuminum or iron containing salt to form a scandium containing stream,and purifying the scandium containing stream to form a scandium compoundend product.

Another embodiment relates to a method of selectively removing scandiumfrom a scandium fluoride containing slurry, comprising adding analuminum containing salt to the scandium fluoride containing slurry toform at least one aluminum fluoride complex and causing the scandiumfluoride to dissolve, removing the at least one aluminum fluoridecomplex from the slurry to provide a scandium containing stream, andpurifying the scandium containing stream to form a scandium compound endproduct.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is incorporated herein and constitutespart of this specification, illustrates exemplary aspects of theinvention. Together with the general description given above and thedetailed description given below, the drawing serves to explain featuresof the invention.

FIG. 1 is a process flow diagram illustrating an overview of the stepsin a method of recovering scandium oxide from a solid material accordingto an embodiment.

FIG. 2 is a process flow diagram illustrating an overview of the stepsin another method of recovering scandium oxide from a solid materialaccording to another embodiment.

DETAILED DESCRIPTION

As used herein, selective removal of an ion or compound generally refersto methods to facilitate the removal of the ion or compound fromsolutions or suspensions (e.g., slurries). As used herein, the selectiveremoval of scandium generally refers to methods to facilitate theremoval of scandium (III) ions (Sc³⁺) or scandium-containing compoundsfrom a solution or suspension.

As used herein, solvent extraction refers to extracting a substance fromone liquid phase (e.g., an aqueous solution) into a different liquidphase (e.g., an organic solvent) based on the relative solubility of thesubstance in each of the phases.

Scandium oxide, and more particularly scandium (III) oxide, is describedherein as the end product of the various embodiment methods. However,scandium(III) oxide is given merely as an example, and the methodsdescribed herein may be used in the production of other useful products,including, but not limited to, non-stoichiometric scandium oxide,scandium(III) chloride (ScCl₃), scandium(III) hydroxide (Sc(OH)₃),scandium(III) oxalate (Sc₂(C₂O₄)₃) and scandium(III) carbonate(Sc(CO₂)₃). One or more of the above scandium compounds may also reducedto produce scandium metal. These products are collectively referred toherein as “scandium compound end products”.

The present inventors realized that while scandium is normally quitesoluble in a highly acidic solution (pH<2), it precipitates as scandiumfluoride (ScF₃) when fluoride is present in the acidic solution.Scandium fluoride is not a desirable intermediate product for formingscandium oxide for commercial uses.

The present inventors have discovered that the addition of aluminumcontaining salts, such as AlCl₃, Al₂(SO₄) or aluminum hydroxide, or ironcontaining salts, such as FeCl₂, FeCl₃ or Fe₂(SO₄)₃, to the solutionreduces or prevents the precipitation of scandium salts. If applicable,the aluminum or iron based salts can also be added as hydrated salts,such that the aluminum containing salts can comprise AlCl₃, Al₂(SO₄) oraluminum hydroxide with or without waters of hydration. The aluminumand/or iron in solution preferentially form complexes with fluorinerelative to scandium, reducing the amount of free fluorine in solution,thereby increasing the concentration of scandium that can stay insolution. By keeping the scandium in solution, the scandium can berecovered in a subsequent purification step, such as a solventextraction or ion exchange process step.

A method for the selective recovery of scandium from a waste acid streamaccording to a first embodiment is illustrated in FIG. 1. In the method100, scandium-containing feed material 102, such as a scandiumcontaining ore, sand or tailings from another mineral recovery process,is provided to a first reactor vessel 104. The first reactor vessel 104may be an acid leaching reactor, such as a tank in which an acidleaching process takes place.

An acid solution 106 is also added to the first reactor vessel 104. Theacid solution 106 is typically an aqueous leaching solution and mayinclude one or more acids. Suitable acids include, but are not limitedto hydrochloric acid, sulfuric acid and nitric acid. Preferably, theacid solution has a pH of 2 or less, such as 1 to 2.

An aluminum containing salt or an iron containing salt is also added. Inan embodiment, the aluminum containing salt or an iron containing saltmay be added to the scandium-containing feed material 102.Alternatively, the aluminum containing salt or an iron containing saltmay be dissolved in the acid solution 106. In another embodiment, thealuminum containing salt or an iron containing salt is separately addedto the first reactor vessel 104.

In an embodiment, an atomic ratio of aluminum or iron added to fluorinein the first reactor is greater than or equal to 3, such as 3 to 20. Inan embodiment, the atomic ratio of aluminum or iron to scandium in thefirst reactor is greater than or equal to 2, such as 2 to 15. Forexample, if the aluminum salt is added to the first reactor vessel, thenfor low fluoride containing feed materials, the atomic ratio of aluminumto scandium can be 2 to 3, while for high fluoride containing feedmaterials, the atomic ratio of aluminum to scandium can be 10 to 12. Inone embodiment, a filter may be located between the two vessels toremove undissolved solids, such as silicates.

A scandium containing stream 110, which can be a scandium containingsolution or a slurry (e.g., flowable suspension containing inertundissolved solids) exits one portion of the first reactor vessel 104.In an embodiment, an amount of aluminum or iron in the first reactorvessel 104 is sufficient to prevent or reduce scandium precipitationfrom the scandium containing stream 110. Tailings 108 comprisingnon-soluble rocks and minerals are removed from the first reactor vessel104 by any suitable method, such filtration or by removal from anotherportion of the first reactor vessel 104. The tailings 108 may bediscarded, processed further to recovery other valuable elements, orrecycled to the front end of the acid leaching reactor if they stillcontain sufficient scandium.

The scandium containing stream 110 may then be passed to second reactorvessel 112. The second reactor vessel 112 may be a purification reactor,such as a tank or ion exchange column, in which the scandium containingstream 110 is purified. That is, the scandium containing stream 110 maybe treated to remove other (non-scandium) soluble elements in thescandium containing stream 110. Other soluble elements include, but arenot limited to, zirconium and titanium. The other soluble elements maybe removed by any suitable process, such as solvent extraction, ionexchange and/or stripping. In an embodiment, the scandium containingstream 110 may be mixed with a scrubbing agent 114 to form a separablecompound 116. For example, zirconium preferentially reacts with oxalicacid (H₂C₂O₄), for example, about 0.3-1.5 M, preferably about 1.1 MH₂C₂O₄, to form the separable oxalate compound 116 that may be separatedfrom the scandium containing stream 110. Titanium preferentially reactswith sulfuric acid (e.g., 0.5-5M H₂SO₄) and hydrogen peroxide (e.g.,2-10%, e.g., 5% H₂O₂) to form a separable titanium sulfate compound 116(e.g., TiO(SO₄)₂ ²⁻). Removal of the soluble elements as the separablecompound 116 provides in a purified scandium containing stream 118exiting the second reactor vessel 112.

In an embodiment, the purified scandium containing stream 118 is apurified loaded organic phase of a solvent extraction process. A stripsolution may then be added to the purified loaded organic phase tounload scandium. The strip solution may be, for example, a sodiumhydroxide (NaOH) solution. Sc³⁺ ions may be unloaded from the loadedorganic phase and into an aqueous phase with Na⁺ and OH⁻, from whichsolid scandium hydroxide (Sc(OH)₃) may precipitate out of solution.Alternatively, the second reactor vessel 112 may be an ion exchangecolumn which is used to extract the purified scandium containing stream118.

As discussed above, the scandium hydroxide may then be leached toextract scandium ions from the filter cake. Then, the extracted sodiumions may be precipitated out of solution as a scandium oxalate productfrom the filtrate. The scandium oxalate product may be calcined anddried to make a product containing scandium oxide (e.g., Sc₂O₃) oranother scandium compound end product.

In an embodiment, impurities may be removed with solvent extraction,such as, cross-current solvent extraction. In embodiments, thescandium-containing stream may be an aqueous phase and the solventstream may be an organic phase. In an embodiment, cross-current solventextraction may be performed as a multistage process using across-current array. A multistage cross-current array may containmultiple extraction units, for example two to six, such as threeextraction units in series. In an embodiment, the extraction units in anarray may be mixing tanks or settlers, or mixer-settler units. Inanother embodiment, extraction units may be centrifugal extractors thatmix and separate in the same unit. In another embodiment, the extractionunits may be separatory funnels.

Methods for the selective recovery of scandium, e.g., scandium compoundend products from fluoride bearing materials are provided. The steps ofthe various embodiments may be combined with other scandium recoveryprocesses, such as described in U.S. patent application Ser. No.14/151,177, filed Jan. 9, 2014, which issued as U.S. Pat. No. 9,102,999,hereby incorporated by reference. The steps of the various embodimentsmay include: solvent extraction (e.g., cross-current solvent extraction)to load at least one stage (e.g., multiple stages) of an organic phasewith scandium ions (e.g., Sc³⁺) from a solution, stripping scandium(e.g., in the form of Sc(OH)₃) from the organic phase and precipitationand filtration of scandium hydroxide (e.g., Sc(OH)₃).

As discussed in U.S. patent application Ser. No. 14/151,177, thescandium hydroxide may then be leached to extract scandium ions from thefilter cake. The extracted sodium ions may then be precipitated out ofsolution as a scandium oxalate product from the filtrate. The scandiumoxalate product may be calcined and dried to make a product containingscandium oxide (e.g., Sc₂O₃). Byproducts of some or all of these stepsmay be recycled back for use in different steps of the process, or maybe converted back into a starting reactant for use in a different stepof the process.

In an alternative second embodiment method 200 illustrated in FIG. 2,fluoride solubility is enhanced prior to scandium acid leaching. Solidmaterials 202 containing scandium and fluoride are initially provided toa pre-reactor 204 and are acid leached with an acid 206 at a mild pH of3 to 5, (e.g. about 4) in the presence of an aluminum salt, such asaluminum chloride or aluminum sulfate.

At mildly acidic pH, scandium solubility is severely limited by thesolubility of scandium hydroxide. However, at mildly acidic conditions,aluminum solubility is not significantly impaired. Thus, aluminumfluoride 208 can form preferentially to scandium fluoride at mildlyacidic pH to decrease the fluorine content available for formingscandium fluoride.

Filtration (or other suitable solid/liquid separation technique, such assettling/decanting, centrifugation, etc.) of the slurry of scandium(still as solids) and fluoride (primarily in the liquid as aluminumfluoride complexes, e.g., AlF₄₋₆) allows the scandium to be segregatedfrom the fluoride 208. The fluoride wash step may be repeated/scaled upby just adding more water and aluminum salt, such as AlCl₃.

Subsequent acid leaching of the fluoride depleted raw material 102 whichare provided from the pre-reactor 204 to the acid leaching reactor 104frees scandium solids.

For example, after removing the aluminum fluoride 208 from thepre-reactor 204, the remaining scandium containing solid 102 may be acidleached in the acid leaching reactor 104 in a highly acidic solution,such as a solution having a pH of 2 or less, such as 1-2 usinghydrochloric, sulfuric and/or nitric acid to recover the scandiumcompound end products, as described above with respect to the firstembodiment.

Thus, in this alternative embodiment, the step of acid leaching includestwo substeps. A first acid leaching substep in the pre-reactor 204 usesan acid having a pH between 3 and 5 to form and remove an aluminumfluoride 208 complex. A subsequent second acid leaching substep in theacid leaching reactor 104 uses the at least one acid having a pH of 2 orless to form the scandium containing stream 110.

In another alternative embodiment, if some or all of the scandium hasprecipitated as ScF₃, the scandium can be recovered from the ScF₃precipitate with the addition of Al and/or Fe salts to the ScF₃containing slurry. The Al and/or Fe form complexes with the fluorine,causing the ScF₃ precipitate to dissolve. In this manner the ScF₃precipitate slurry can be made into a clear solution from which scandiumis subsequently recovered as scandium compound end products. Thisapproach can be used to solubilize scandium from any material in whichscandium fluoride precipitation is an issue.

Thus, in this alternative embodiment, a method of selectively removingscandium from a scandium fluoride containing slurry includes adding analuminum containing salt to the scandium fluoride containing slurry toform at least one aluminum fluoride complex and causing the scandiumfluoride to dissolve, removing the at least one aluminum fluoridecomplex from the slurry to provide a scandium containing stream (e.g.,solution or slurry), and purifying the scandium containing stream toform a scandium compound end product.

As is understood in the art, not all equipment or apparatuses are shownin the figures. For example, one of skill in the art would recognizethat various holding tanks and/or pumps and/or filters may be employedin the present method.

The foregoing method descriptions and the process flow diagrams areprovided merely as illustrative examples and are not intended to requireor imply that the steps of the various embodiments must be performed inthe order presented. As will be appreciated by one of skill in the artthe steps in the foregoing embodiments may be performed in any order.Words such as “then,” “next,” etc. are not intended to limit the orderof the steps; these words are simply used to guide the reader throughthe description of the methods. Although process flow diagrams maydescribe the steps as a sequential process, many of the steps can beperformed in parallel or concurrently.

Any reference to claim elements in the singular, for example, using thearticles “a,” “an” or “the” is not to be construed as limiting theelement to the singular.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the following claims and theprinciples and novel features disclosed herein.

1. A method of selectively removing scandium from a scandium-containingfeed material, comprising: providing the scandium-containing feedmaterial; acid leaching the scandium-containing feed material with atleast one acid in a presence of at least one of an aluminum or ironcontaining salt to form a scandium containing stream; and purifying thescandium containing stream to form a scandium compound end product. 2.The method of claim 1, wherein the at least one of the aluminumcontaining salt or the iron containing salt is added to thescandium-containing feed material prior to the step of acid leaching. 3.The method of claim 1, wherein the at least one of the aluminumcontaining salt or the iron containing salt is dissolved in a solutioncomprising the least one acid.
 4. The method of claim 1, wherein the atleast one of the aluminum containing salt or the iron containing salt isseparately added to a reactor vessel in which the acid leaching takesplace.
 5. The method of claim 1, wherein the at least one acid isselected from at least one of hydrochloric acid, sulfuric acid andnitric acid.
 6. The method of claim 1, wherein the scandium compound endproduct comprises scandium hydroxide, scandium oxide, scandium chloride,scandium oxalate or scandium carbonate.
 7. The method of claim 1,wherein the step of purifying comprises at least one of solventextraction, ion exchange and stripping.
 8. The method of claim 1,wherein the scandium-containing feed material comprises a solid materialcontaining fluorine which forms a complex with aluminum ions or ironions during the acid leaching.
 9. The method of claim 8, wherein anamount of aluminum or iron in a reactor vessel in which the acidleaching takes place is sufficient to prevent scandium precipitation.10. The method of claim 1, wherein the step of acid leaching thescandium-containing feed material with at least one acid takes place inthe presence of the aluminum containing salt.
 11. The method of claim10, wherein the aluminum containing salt is AlCl₃ with or without watersof hydration.
 12. The method of claim 10, wherein the aluminumcontaining salt comprises Al₂(SO₄) with or without waters of hydration,or aluminum hydroxide with or without waters of hydration.
 13. Themethod of claim 10, wherein an atomic ratio of aluminum to fluorine isgreater than or equal to 3 in a reactor vessel in which the acidleaching takes place.
 14. The method of claim 13, wherein the atomicratio of aluminum to scandium in the reactor vessel in which the acidleaching takes place is greater than or equal to
 2. 15. The method ofclaim 10, wherein the at least one acid has a pH of 2 or less during thestep of acid leaching.
 16. The method of claim 10, wherein the step ofacid leaching comprises: a first acid leaching substep using an acidhaving a pH between 3 and 5 to form and remove an aluminum fluoridecomplex; and a subsequent second acid leaching substep using the atleast one acid having a pH of 2 or less to form the scandium containingstream.
 17. A method of selectively removing scandium from a scandiumfluoride containing slurry, comprising: adding an aluminum containingsalt to the scandium fluoride containing slurry to form at least onealuminum fluoride complex and causing the scandium fluoride to dissolve;removing the at least one aluminum fluoride complex from the slurry toprovide a scandium containing stream; and purifying the scandiumcontaining stream to form a scandium compound end product.
 18. Themethod of claim 17, wherein the aluminum containing salt is AlCl₃ withor without waters of hydration.
 19. The method of claim 17, wherein thealuminum containing salt is Al₂(SO₄) with or without waters ofhydration.
 20. The method of claim 17, wherein: the scandium compoundend product comprises scandium hydroxide, scandium oxide, scandiumchloride, scandium oxalate or scandium carbonate; and the step ofpurifying comprises at least one solvent extraction, ion exchange andstripping.